Polarization is a property of certain types of waves that describes the orientation of their oscillations. Electromagnetic waves including visible light can exhibit polarization. By convention, the polarization of light is described by specifying the orientation of the light's electric field at a point in space over one period of the oscillation. When light travels in free space, in most cases it propagates as a transverse wave, i.e. the polarization is perpendicular to the light's direction of travel. In this case, the electric field may be oriented in a single direction (linear polarization), or it may rotate as the wave travels (circular or elliptical polarization). In the latter cases, the oscillations can rotate either towards the right or towards the left in the direction of travel. Depending on which rotation is present in a given wave it is called the wave's chirality or handedness. Polarization of fully polarized light can be represented by a Jones vector. The x and y components of the complex amplitude of the electric field of light travel along z-direction, Ex(t) and Ey(t), are represented as
      (                                                      E              x                        ⁡                          (              t              )                                                                                      E              y                        ⁡                          (              t              )                                            )    =                    E        0            ⁡              (                                                                              E                                      0                    ⁢                    x                                                  ⁢                                  ⅇ                                      ⅈ                    ⁡                                          (                                              kz                        -                                                  ω                          ⁢                                                                                                          ⁢                          t                                                +                                                  ϕ                          x                                                                    )                                                                                                                                                                E                                      0                    ⁢                    y                                                  ⁢                                  ⅇ                                      ⅈ                    ⁡                                          (                                              kz                        -                                                  ω                          ⁢                                                                                                          ⁢                          t                                                +                                                  ϕ                          x                                                                    )                                                                                                          )              =                  E        0            ⁢                                    ⅇ                          ⅈ              ⁡                              (                                  kz                  -                                      ω                    ⁢                                                                                  ⁢                    t                                                  )                                              ⁡                      (                                                                                                      E                                              0                        ⁢                        x                                                              ⁢                                          ⅇ                                              ⅈϕ                        x                                                                                                                                                                                    E                                              0                        ⁢                        y                                                              ⁢                                          ⅇ                                              ⅈϕ                        y                                                                                                                  )                          ·                  (                                                                                          E                                          0                      ⁢                      x                                                        ⁢                                      ⅇ                                          ⅈϕ                      x                                                                                                                                                                E                                          0                      ⁢                      y                                                        ⁢                                      ⅇ                                          ⅈϕ                      y                                                                                                    )                    is the Jones vector. Polarization of light with any polarization, including unpolarized, partially polarized, and fully polarized light, can be described by the Stokes parameters, which are four mutually independent parameters.
A device that can detect polarization of light, or even measure the light's Jones vector or Stokes parameters can be useful in many application.